10.1002/ejoc.202000222
European Journal of Organic Chemistry
COMMUNICATION
A 10-mL reaction tube was charged with sulfoxide 1 (0.50 mmol), B2cat2
(0.13 g, 0.55 mmol), and toluene (1.2 mL) under air. The resulting
mixture was stirred at 100 °C for 8 h. The mixture was directly passed
through a pad of alumina (8.8 g, ϕ = 22 mm, H = 25 mm) with ethyl
acetate (20 mL) as an eluent, and concentrated under reduced pressure
to give product 2. If necessary, purification was done by column
chromatography on silica gel (hexane/ethyl acetate).
that electron-rich sulfoxides reacted faster than electron-poor
ones. This implies that the easier the complexation of a sulfoxide
to a diboron is, the faster the reaction proceeds.
Acknowledgements
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This work was supported by JSPS KAKENHI Grant Numbers
JP16H04109, JP18H04254, JP18H04409, JP19H00895, and
JP18K14212 as well as JST CREST Grant Number
JPMJCR19R4. We also thank CENTRAL GLASS CO., LTD. for
providing (CF3)2CHOH.
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20
10
0
2a
2c
2e
Keywords: Bis(catecholato)diboron • Chemoselective •
Reduction • Sulfide • Sulfoxide
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0
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time (h)
Figure 1. Reaction time profile according to the para-substituents on diaryl
sulfoxides
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As is shown in Scheme 3, the reaction would be initiated
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2
accompanied by the formation of
(catB)2O.[15a] To facilitate the formation of A, the use of B2cat2,
more Lewis acidic than B2pin2 and B2nep2, would be vital. Given
the time profile depicted in Figure 1, electron-rich sulfoxides
would shift the equilibrium toward A, which resulted in
acceleration of the reaction.
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Scheme 3. A possible mechanism.
In conclusion, we have developed an efficient and
operationally simple method for reduction of sulfoxides to
sulfides with B2cat2 as a reducing agent. This user-friendly
protocol is characterized by high functional group tolerance and
easy purification process.
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Experimental Section
General procedure for the reduction of sulfoxides 1
3
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